The present invention relates to an elevator group supervisory control system and in particular to control of elevator assignment to generated hall calls.
An elevator group supervisory control system treats multiple elevator cages as one group to provide more efficient transport service to users. Specifically, four to eight elevator cages are typically controlled as one group. If a hall call occurs at a floor, the most appropriate one is selected from this group and assigned to the hall call.
Assignment control based on an assignment evaluation function of waiting time, which constitutes the basic assignment control principle of existing group supervisory control systems, was developed around 1980 when microcomputers were introduced. In this method, yet-to-be served hall calls are kept under management. If a new hall call occurs, the time for which the new hall call would wait until served is calculated for each cage according to the predicted waiting time of each yet-to-be served hall call. Consequently, the new hall call is assigned to either a cage that requires the shortest waiting time or a cage that is not to serve a hall call which has long been pendent. This control principle, determining call assignment according to an evaluation function of predicted waiting time, provided an epoch-making control method in those days and has been inherited to the present elevator makers for group supervisory control. However, this control has the following two problems:                1) Optimum cage assignment is determined based only on the yet-to-be served hall calls. Influence on future assignments is not taken into consideration.        2) Assignment is made to a cage which minimize the evaluation function where no cage-to-cage spatial relation is considered. There is no concept of cooperation among the cages.        
To solve these problems with the aforementioned assignment method using an evaluation function of predicted waiting time, a variety of control methods have so far been proposed. To be brief, their basic policies are to control the respective cages so as to arrange them at temporally equal intervals. If the respective cages are not evenly distributed, that is, some is temporally distant from another, a hall call occurring between them is likely to wait long until served. If the respective cages are arranged at temporally equal intervals, it is possible to prevent long waits. The conventional control methods which are aimed at temporally equal interval arrangement are listed below.
1) Equal interval-prioritized zone control (disclosed in JP-A-1-226676)
2) Equal interval-prioritized zone/Inhibited zone control (disclosed in JP-A-7-117941)
In each of these two methods, a priority zone consisting of some served floors and an inhibited zone of other served floors are set to each car. If a new hall call occurs in the priority zone of a cage, the evaluation value is manipulated so as to raise the probability of the hall call being assigned to the cage. In the case of a new hall call in the inhibited zone, the evaluation value is manipulated so as to lower the probability of assignment. This intends to make the respective cages closer to a temporally equal interval state.
3) Temporally equal interval-considered assignment-evaluated control (disclosed in JP-B-7-72059)
The position of each cage at a future point of time is predicted. Accordingly, cage-to-cage temporal intervals at that time are predicted. The assignment limiting evaluation value is calculated from this predicted cage-to-cage intervals. This evaluation value is used to control assignments to prevent many cages from being assigned to specific floors. This intends to consequently make the cage-to-cage intervals more temporally even.
4) Assignment correction by making service availability time distribution uniform (disclosed in WO98/45204)
This basic concept is similar to the method 3). The arrangement of the respective cages at a future point of time is predicted. From the predicted cage arrangement, the fastest time of arrival at each floor is calculated as the service availability time. Further, the service availability time distribution is calculated. The hall call assignment evaluation values are corrected so as to make the service availability time distribution uniform. This intends to consequently make the service availability time constant not depending on the floor.
5) Position evaluation value-used assignment method (JP-A-2000-118890)
In this method, a position evaluation value to prevent cages from clustering is calculated for each cage. Assignment to a hall call is determined using a position evaluation-included assignment evaluation value. The position evaluation value of a cage is calculated based on the relation between its absolute position and the average absolute position of the other cages when the hall call is generated. This method also intends to evenly arrange the respective cages.
However, the above-listed prior art techniques do not substantially solve the problem of arranging the cages evenly to attain equal interval condition. Since cage-to-cage intervals/positioning are evaluated only at one point of time, the aforementioned prior art techniques are difficult to stably keep the respective elevator cage in temporally equal interval state over a long period of time.